1. Technical Field
The present invention particularly relates to a throttle valve control device which is capable of fine control of the amount of intake air required for idling operation in an internal combustion engine.
2. Background Art
In internal combustion engines used in automobiles, the idling operation in particular requires fine control of the amount of intake air in accordance with the temperature conditions of the environment and equipment, and in accordance with the conditions of use of peripheral equipment such as air conditioning and the like. In the past, various proposals have been made regarding such control.
For example, there is a method in which a bypass air passage is formed parallel to the throttle valve, a flow rate control valve is installed at an intermediate point in this bypass air passage, and the amount of air that flows through the bypass air passage is controlled by this valve.
However, in the case of this control method, a safety measure is taken in which the inflow into the bypass air passage is restricted by a temperature-sensing element utilizing the temperature during engine warm-up in order to prevent an unnecessarily large amount of intake air from being supplied to the engine as a result of trouble with the actuator that drives the flow rate control valve. As a result, the structure of the apparatus is complicated.
Accordingly, a method has been devised in which the throttle valve is directly driven by a DC motor or the like in the low-opening region of the throttle valve, i.e., the so-called idle speed control (ISC) region (hereafter referred to as the ISC region).
FIG. 5 shows a universally known example of such a throttle valve control device; this figure is a diagram which shows the construction of the device in schematic form. The throttle valve 1 is mounted inside the bore of a throttle body (not shown in the figures) by means of a throttle shaft 2, so that the throttle valve 1 can rotate in either the opening or closing direction as indicated by the arrows(while the arrows are linear in the drawings in the application, it is understood that the movement represented in the schematic drawings of this application is rotational). A first lever 3 and second lever 4 are attached to respective ends of the throttle shaft 2.
The second lever 4 is loosely mounted inside a space between walls 5a and 5b formed in a throttle lever 5. The first lever 3 contacts a free lever 6, and the free lever 6 is integrally connected to a DC motor 7 via a gear speed-reduction device (not shown in the figures).
One end of a first spring 9 and one end of a second spring 10 are connected to the throttle body 8. The other end of the first spring 9 is anchored on the free lever 6, and the other and of the second spring 10 is anchored on the second lever 4.
The fully open position of the throttle lever 5 is regulated by a xe2x80x9cfully-openxe2x80x9d stopper 11, and the initial position of idling (when no electric power is applied) is determined by an idling stopper 12. Furthermore, the upper limit position of ISC is regulated by an ISC stopper 13, and the ISC stopper 13 is disposed in a position located at a far lower degree of opening than the xe2x80x9cfully-openxe2x80x9d stopper 11.
The idling stopper 12 has a spring 12a inside, and the initial position of idling can be adjusted by adjusting a movable stopper 12b by means of a screw or the like (not shown in the figures). Furthermore, the internal spring 12a is set at a value that is equal to or greater than the synthesized value of the first return spring 9 and second return spring 10, so that when the DC motor 7 is not powered, the degree of opening of the throttle valve is determined by the position that is set by the movable stopper 12b of the idling stopper 12.
The operation of the accelerator pedal during normal operation (of the vehicle) is transmitted to the throttle lever 5 via a throttle link. When the throttle lever 5 moves in the opening direction, the wall 5a quickly contacts the second lever 4, thus moving the second lever 4 against the driving force of the second spring 10, and this movement acts on the throttle valve 1 via the throttle shaft 2 so that the valve opens. With the throttle valve 1 open, an operation by means of the accelerator pedal can be performed until the throttle lever 5 contacts the xe2x80x9cfully-openxe2x80x9d stopper 11.
When the depression of the accelerator pedal is relaxed from the fully open position of the throttle valve 1, the throttle valve 1 is pulled back by the second return spring 10 in a state in which the wall Sa of the throttle lever 5 and the second lever 4 are in contact, so that the throttle valve 1 moves in the closing direction. The first lever 3 then quickly contacts the free lever 6 and stops. The throttle lever 5 is caused to remain static by a link (not shown in the figures), and even if the movable stopper 12b is displaced, the second lever 4 is between the walls 5a and 5b, so that the position of the throttle lever 5 does not change.
In ISC, the DC motor 7 is driven so that the first lever 3 is driven in the opening or closing direction via a gear train. Since the driving force of the DC motor 7 is greater than the force of the internal spring 12a of the idling stopper 12, the throttle valve can also be set at a degree of opening that is less than that of the movable stopper 12b. Movement in the opening direction is limited by the ISC stopper 13.
As a result of the abovementioned construction, the degree of opening can be freely adjusted by the DC motor 7 between the idling stopper 12 and the ISC stopper 13. Outside this range, the degree of opening of the throttle valve is determined by the accelerator pedal operation of the driver.
In the abovementioned conventional example, the degree of opening of the throttle valve 1 when power is not applied is ensured, and the throttle valve can be directly controlled by the DC motor in the low-opening region in a range of L1. Accordingly, a bypass air passage is unnecessary.
However, in the abovementioned example, two return springs are needed, i.e., a first return spring and a second return spring, as opposed to a single return spring in a conventional device. As a result, the structure of the throttle body is complicated.
Furthermore, when the free lever 6 is moved by the DC motor, the driving forces of the two return springs or the internal spring 12a increase in accordance with the amount of movement, so that a variation occurs in which the driving forces are different in the opening and closing directions. As a result, control of the degree of throttle opening by the motor current is difficult, and the control circuit becomes complicated. Moreover, the motor must have a large output in order to overcome the driving force of the springs, and this leads to the problems of increased size and increased cost of the apparatus.
The present invention solves the abovementioned problems. It is an object of the present invention to provide a throttle valve control device which has a simple structure, and which can be made compact.
In order to achieve the abovementioned object, the throttle valve control device of the present invention comprises a structural body in which a throttle valve which is disposed inside the bore of a throttle body, a throttle shaft which supports the throttle valve so that this throttle valve is free to pivot, and a throttle lever that pivots the throttle shaft, are integrally connected. A return spring has one end anchored to the structural body and urges the throttle valve so that the throttle valve rotates in the closing direction. A free lever is supported on the throttle shaft so that this free lever is free to pivot, anchors the other end of the return spring, and can contact and move away from the structural body. An actuator drives the free lever. The driving of the free lever by the actuator causes the structural body to pivot, so that the throttle valve is opened and closed.
A construction may be used in which the actuator opens and closes the throttle valve within the ISC region.
Furthermore, a construction may be used in which the actuator has a stator including a magnetic flux generating part, around which an electromagnetic coil is wound so that magnetic flux is generated, and a magnetic field forming part which has three magnetic pole pieces on more or less the same straight line, and which distributes the magnetic flux so that two magnetic field regions are formed. A slider advances and retracts parallel to a line connecting the magnetic pole pieces in accordance with the magnetic field regions, and is equipped with magnetic members that have two magnetic surfaces of mutually different polarities in the advance and retraction direction, and a magnetic path member.